In brushes of this type, the bristles generally define a substantially helicoid nappe, and the ends of the bristles are arranged in the form of spirals. As a result, the brush does not fill homogeneously with the makeup product, nor can the eyelashes or hair easily penetrate to the interior of the nappe defined by the bristles of the brush. Because of this, the made-up eyelashes are often poorly separated and are instead joined in tufts; for more careful makeup, considerable time must be spent.